1. Field of the Invention
The present invention relates to a magnetoresistive (MR) effect element for detecting external magnetic fields such as signal fields and showing the resistance change corresponding to the field intensity, a thin-film magnetic head having the MR effect element, a head gimbal assembly (HGA) having the thin-film magnetic head and a magnetic disk drive apparatus having the HGA. Further, the present invention relates to a manufacturing method of a thin-film magnetic head wafer and a thin-film magnetic head having the MR effect element.
2. Description of the Related Art
Responding to larger capacity storage and further miniaturization of a magnetic disk drive apparatus in recent days, a giant magnetoresistive (GMR) head is being aggressively improved, which has a read head element utilizing a GMR effect and shows high sensitivity and high output. Furthermore, responding to much higher density recording, a tunnel magnetoresistive (TMR) head is under intense development, which has a read head element utilizing a TMR effect that is expected to show two times or more larger MR ratio than that of the GMR effect.
The structures of the TMR head and the commonly used GMR head are different from each other due to the difference in the flow direction of sense currents. While the commonly used GMR head has a current-in-plane (CIP) structure in which a sense current flows in the direction parallel to the stacking plane of the MR effect multilayer, the TMR head has a current-perpendicular-to-plane (CPP) structure in which a sense current flows in the direction perpendicular to the stacking plane. Recently, a GMR head having the CPP structure (CPP-type GMR head (CPP-GMR head)) is also developed as described in Japanese patent Publication No. 05-275769A. As the CPP-GMR head, developed is a head having a spin-valve magnetic multilayer film such as, for example, a specular-type magnetic multilayer film or a dual spin-valve-type magnetic multilayer film, as is the case in the CIP-GMR head.
Currently, a serious problem occurs in the CIP structure that an insufficient insulation is likely to occur between the MR effect multilayer and magnetic shield layers due to narrowing the read-gap corresponding to higher density recording. On the contrary, the CPP structure uses the magnetic shield layers as electrodes and needs no insulating means between the MR effect multilayer and the magnetic shield layers. As a result, the CPP structure is free from the above problem of the CIP structure. Consequently, the CPP structure has a significant advantage over the CIP structure.
As just described, the CPP-GMR head and the TMR head has a structure in which the MR effect multilayer is sandwiched directly between upper and lower electrode layers also acting as shield layers. In the CPP structure, an insulating layer is provided so as to surround the side surfaces of the MR effect multilayer for the purpose of preventing a short-circuit of sense currents between the upper and lower electrode layers. However, the insulating layer sandwiched between the upper and lower electrode layers generates a corresponding capacitance which has a possibility to cause a degradation of the reading performance or a breakdown of the element through the influence of disturbance noise or electrostatic discharge (ESD) phenomenon, as shown, for example, Japanese patent Publication No. 2005-50418A. Therefore, in view of the suppression of the capacitance, the insulating layer is required to have larger thickness. Further, in the case where the upper and lower electrode layers has a large opposed area, the insulating layer is also required to have larger thickness to decrease the occurrence possibility of a short-circuit by pinholes in the insulating layer.
Further, in the CPP structure, U.S. Pat. No. 6,381,107 describes a technique in which a part of the shield layer is provided on the rear side of the MR effect multilayer, which plays a role as a back flux-guide for improving reading performance. FIG. 15 shows an embodiment described in U.S. Pat. No. 6,381,107. As shown in FIG. 15, an insulating layer 1501 is formed on a lower electrode layer 1500 and on the rear side surface of an MR effect multilayer 1503 to prevent a short-circuit between the lower electrode layer 1500 and the upper electrode layer 1502. In the embodiment, because the distance between the rear end of a free layer 1504 and the upper electrode layer 1502 acting as a back flux-guide becomes much smaller, a magnetic flux from a recording bit of the magnetic disk can easily reach the MR effect multilayer by being guided by the back flux-guide. As a result, the back flux-guide is expected to effect a sufficient resistance change corresponding to the intrinsic MR effect of the MR effect multilayer.
However, a conventional structure having the above described back flux-guide has a possibility of a degradation of reading performance or a breakdown of the element due to the increase in the above-described capacitance between the upper and lower electrode layers.
In the structure, in order to obtain the sufficient back flux-guide effect, the distance between the rear end of the free layer and the upper electrode layer is required to be smaller with the thickness of the insulating layer smaller. However, the structure of such a thin insulating layer is likely to cause the disturbance noise or the ESD phenomenon as described above, and has some possibility of a degradation of the reading performance or a breakdown of the element.
Meanwhile, it may be one of the measures against this problem to increase the thickness of the insulating layer 1501 only on the lower electrode layer 1500 under the condition of keeping the thickness on the rear side surface of the MR effect multilayer 1503. However, the thickness of the insulating layer 1501 on the lower electrode layer 1500 can not be set to a sufficiently large value under the restriction for obtaining the desired back flux-guide effect, which is difficult to reduce the capacitance effectively.